Ischemic Necrosis of Bone (INB) is a frequent complication of systemic lupus erythematosus, rheumatoid arthritis and corticosteroid therapy. We propose to study patients in these high risk groups as to prevalence and disease-associated risk factors. By prospectively comparing different non-invasive diagnostic tests (routine roentgenograms, bone and bone marrow scintigraphy) we will define the sensitivity and specificity of each. In those patients detected by the above screening techniques, intraosseous pressure measurements and venography will be carried out to determine the specificity and predictive capability of these tests. Patients with early INB will be systematically randomized for medical (protected weight-bearing) or surgical (core decompression) treatment, to compare their relative efficacy. In the laboratory portion we propose to use the radioactive tracer microsphere method in addition to intraosseous pressure, fluorochrome labeling and routine histology to assess: a) The changes in bone blood flow in an extended animal model of INB (lipiodol embolization); b) The influence of corticosteroid administration and the sympathetic nervous system alone and in combination on bone blood flow; and c) the effect on bone blood flow of core decompression of normal and ischemic bone. The interdisciplinary approach should lead to a better understanding of the pathogenesis of INB, leading to earlier diagnosis and more effective treatment.